1. Field of the Invention
The invention relates to the field of test fixtures for electrically contacting electrical components in order to measure the electrical parameters of the components.
2. Prior Art
The prior art is replete with component parameter test equipment designed for testing electrical components such as resistors, capacitors, inductors and so forth. These component testers include, or will accommodate, many types of contact fixtures designed for holding the flexible leads of leaded components. Some of these component holders feature automatic component insertion and removal while others are designed for rapid insertion and removal of the components by the operator.
Some of this test equipment employs Kelvin testing. In Kelvin testing, each lead of the component to be tested makes contact with two contacts of the test bridge. The test bridge provides a drive signal to the component under test through a first one of these contacts. A sensing signal is provided to the bridge through the second of these contacts. The sensing contacts of the bridge are connected to high impedance circuits within the bridge so that they draw very little current thereby minimizing the effect of any contact resistance on the signal transmitted from the component to the test circuitry of the bridge. Contact resistance between the drive signal contacts of the bridge and the leads of the component under test produce a minimal effect on the parameter values measured by the bridge because the contact resistance and inductance of these contacts is not included within the test loop of the bridge.
Despite the high degree of sophistication of test equipment for leaded components, the testing of miniature, leadless components has been a haphazard, jury-rigged affair. Among the known techniques for the testing of miniature leadless components is the use of alligator clips for contacting the individual terminals of the device to be tested. Such a procedure is tedious, time consuming and of questionable accuracy, especially when components as small as 1/16 of an inch (.about.1.59 millimeters) long by 1/32 of an inch (.about.0.79 millimeter) square are to be tested. It is extremely difficult to make good temporary contact to such small components for performing incoming inspection tests to assure that they meet their specifications.
U.S. Pat. Nos. 3,971,618 and 4,075,556 each disclose a test fixture designed for testing miniature leadless components. These systems fail to assure the creation of reliable contact between the test fixture and the component to be tested and thus fail to assure that inaccuracies will not be introduced into the measurements.
Inaccurate testing of such miniature components is a substantial problem because these components are often incorporated in high reliability circuits such as hybrid heart pacemaker units, ground falt interruptor circuits and other similar systems where system failure can cause the immediate death of the wearer or severe injury or death to the user of the system.
An improved system for testing these miniature components is needed in order that measurement accuracy may be assured with a consequent increase in the yield of assembled systems and an increase in the reliability of such systems.